Carbon nanotube composite and method for forming same

ABSTRACT

A method for forming a carbon nanotube composite includes the following steps. A substrate having a surface is provided. A carbon nanotube structure is disposed on the surface of the substrate. The carbon nanotube structure includes a number of carbon nanotubes. The carbon nanotubes define a number of micro gaps. The substrate and the carbon nanotube structure are disposed in an environment filled with electromagnetic waves such that the surface of the substrate is melted and is permeated into the micro gaps.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201110082160.1, filed on Apr. 1, 2011 inthe China Intellectual Property Office, disclosure of which isincorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a carbon nanotube composite and amethod for forming the carbon nanotube composite.

2. Description of Related Art

Carbon nanotubes are a novel carbonaceous material having extremelysmall size and extremely large specific surface area. Carbon nanotubeshave interesting and potentially useful electrical and mechanicalproperties, and have been widely used in various fields such asemitters, gas storage and separation, chemical sensors, and highstrength composites.

However, one main obstacle in applying carbon nanotubes is thedifficulty in processing the common powder form of the carbon nanotubeproducts. Therefore, forming separate and tiny carbon nanotubes intomanipulative carbon nanotube structures is necessary.

Carbon nanotube composite is one kind of manipulable carbon nanotubestructures. A method for producing carbon nanotube composites includes astirring step or vibration step to disperse carbon nanotube powder inthe composite. However, carbon nanotubes have extremely high surfaceenergy and are prone to aggregate. Therefore, it is very difficult toachieve a composite with carbon nanotubes evenly dispersed therein.Furthermore, the carbon nanotubes dispersed in the carbon nanotubecomposite produced by this method, results in a surface of the carbonnanotube composite with low conductivity, thereby limiting theapplication of the carbon nanotube composite.

What is needed, therefore, is to provide a carbon nanotube composite anda method for forming the same that can overcome the above-describedshortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with referenceto the drawings. The components in the drawings are not necessarilydrawn to scale, the emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the views.

FIG. 1 is a flow chart of one embodiment of a method for forming acarbon nanotube composite.

FIG. 2 is a schematic view of one embodiment of a substrate and a carbonnanotube structure.

FIG. 3 is a cross-sectional view of one embodiment of a carbon nanotubecomposite.

FIG. 4 is similar to FIG. 3, but viewed from another perspective.

FIG. 5 shows an image of a surface of the carbon nanotube composite anda magnified image of part of the surface of the carbon nanotubecomposite.

FIG. 6 shows a scanning electron microscope (SEM) image of a top surfaceof the carbon nanotube composite.

FIG. 7 shows an SEM image of a side surface of the carbon nanotubecomposite.

FIG. 8 shows an image of the wetting quality of the carbon nanotubestructure disposed on a surface of the substrate exposed to microwavesand an image of the wetting quality of the carbon nanotube structuredisposed on the surface of the substrate without exposure to microwaves.

FIG. 9 is a waveform chart of a sheet resistance characteristic curve ofthe carbon nanotube composite.

FIG. 10 is a flow chart of one embodiment of a method for forming anelectrode board.

FIG. 11 is a flow chart of another embodiment of a method for forming anelectrode board.

FIG. 12 is a schematic view of one embodiment of an electrode board.

FIG. 13 is a flow chart of one embodiment of a method for forming atouch panel.

FIG. 14 is a schematic view of one embodiment of a touch panel.

FIG. 15 is another schematic view of the touch panel shown in FIG. 14.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIG. 1 and FIG. 2, a method for forming a carbon nanotubecomposite includes:

(a) providing a substrate 300 having a surface 301;

(b) disposing a carbon nanotube structure 304 on the surface 301 of thesubstrate 300; and

(c) disposing the substrate 300 and the carbon nanotube structure 304 inan environment filled with electromagnetic waves.

In step (a), the substrate 300 can be made of ceramic, glass, apolymeric material, or a macromolecular material. Examples of thepolymeric material include polyethylene, epoxy, bismaleimide resin,cyanate resin, polypropylene, polyethylene, polyvinyl alcohol,polystyrene, polycarbonate, and polymethylmethacrylate. The shape of thesubstrate 300 is not limited. The surface 301 of the substrate 300 canbe planar or a curved surface. In one embodiment, the substrate 300 is acuboid made of polyethylene, a thickness of the substrate 300 is about 3millimeters, the surface 301 of the substrate 300 is planar, and a sideof the surface 301 is about 50 millimeters.

In the step (b), the carbon nanotube structure 304 includes a number ofcarbon nanotubes combined by van der Waals force therebetween. Thecarbon nanotubes define a number of micro gaps. The carbon nanotubestructure 304 can be a substantially pure structure of carbon nanotubes,with few impurities. The heat capacity per unit area of the carbonnanotube structure 304 can be less than 2×10⁻⁴ J/m²*K. In oneembodiment, the heat capacity per unit area of the carbon nanotubestructure 304 is equal to or less than 1.7×10-6 J/m²*K. Because the heatcapacity of the carbon nanotube structure 304 is very low, the carbonnanotube structure 304 has a high heating efficiency, a high responseheating speed, and high accuracy. Furthermore, the carbon nanotubes ofthe carbon nanotube structure 304 have a low density of about 1.35g/cm³, so the carbon nanotube structure 304 is light. The carbonnanotubes of the carbon nanotube structure 304 define a number of microgaps. Diameters of these micro gaps can be less than 10 micrometers.Because the carbon nanotubes have a large specific surface area and thecarbon nanotube structure includes a plurality of micropores, the carbonnanotube structure 304 with a number of carbon nanotubes has largespecific surface area. If the specific surface of the carbon nanotubestructure 304 is large enough, the carbon nanotube structure 304 isadhesive and can be directly applied to a surface. The carbon nanotubestructure 304 can be adhered on the surface directly without extraadhesive material.

The carbon nanotubes of the carbon nanotube structure 304 can be orderlyor disorderly arranged. The term ‘disordered carbon nanotube structure’refers to a structure where the carbon nanotubes are arranged alongdifferent directions, and the alignment directions of the carbonnanotubes are random. The carbon nanotubes arranged along each differentdirection can be almost the same (e.g. uniformly disordered). Thedisordered carbon nanotube structure can be isotropic, namely the carbonnanotube film has properties identical in all directions of the carbonnanotube film. The carbon nanotubes in the disordered carbon nanotubestructure can be entangled with each other.

The carbon nanotube structure 304 can be an ordered carbon nanotubestructure. The term ‘ordered carbon nanotube structure’ refers to astructure where the carbon nanotubes are arranged in a consistentlysystematic manner, e.g., the carbon nanotubes are arranged approximatelyalong a same direction and/or have two or more sections within each ofwhich the carbon nanotubes are arranged approximately along a samedirection (different sections can have different directions). The carbonnanotubes in the carbon nanotube structure 304 can be single-walled,double-walled, and/or multi-walled carbon nanotubes. The carbon nanotubestructure 304 includes at least one carbon nanotube film. The carbonnanotube film can be a drawn carbon nanotube film, a pressed carbonnanotube film, or a flocculated carbon nanotube film.

The drawn carbon nanotube film includes a number of successive andoriented carbon nanotubes joined end-to-end by van der Waals forcetherebetween. The drawn carbon nanotube film is a free-standing film,meaning that that the drawn carbon nanotube film does not have to besupported by a substrate and can sustain the weight of itself when it ishoisted by a portion thereof without tearing. A method of making a drawncarbon nanotube film includes:

(b1) providing a carbon nanotube array including a number of carbonnanotubes; and

(b2) pulling out at least a drawn carbon nanotube film from the carbonnanotube array.

In the step (b1), a method of making the carbon nanotube array includes:

(b11) providing a substantially flat and smooth substrate;

(b12) applying a catalyst layer on the substrate;

(b13) annealing the substrate with the catalyst at a temperature in arange from about 700° C. to about 900° C. in air for about 30 minutes toabout 90 minutes;

(b14) heating the substrate with the catalyst at a temperature in arange from about 500° C. to about 740° C. in a furnace with a protectivegas therein; and

(b15) supplying a carbon source gas to the furnace for about 5 minutesto about 30 minutes and growing a super-aligned carbon nanotube arraythat includes the carbon nanotubes from the substrate.

In the step (b11), the substrate can be a P or N-type silicon wafer. Inone embodiment, a 4-inch P-type silicon wafer is used as the substrate.

In the step (b12), the catalyst can be made of iron (Fe), cobalt (Co),nickel (Ni), or any combination thereof.

In the step (b14), the protective gas can be made up of at least one ofnitrogen (N₂), ammonia (NH₃), and a noble gas.

In the step (b15), the carbon source gas can be a hydrocarbon gas, suchas ethylene (C₂H₄), methane (CH₄), acetylene (C₂H₂), ethane (C₂H₆), orany combination thereof.

In the step (b2), the drawn carbon nanotube film can be fabricated by:

(b21) selecting one or more carbon nanotubes having a predeterminedwidth from the carbon nanotube array; and

(b22) pulling the carbon nanotubes to obtain nanotube segments at asubstantially even/uniform speed to achieve a uniform carbon nanotubefilm.

In the step (b21), the carbon nanotube segment includes a number ofsubstantially parallel carbon nanotubes. The carbon nanotube segmentscan be selected by using a tool, such as an adhesive tape, to contactthe super-aligned carbon nanotube array including the carbon nanotubes.In the step (b22), the pulling direction can be substantiallyperpendicular to the growing direction of the super-aligned carbonnanotube array including the carbon nanotubes.

More specifically, during the pulling process, as the initial carbonnanotube segments are drawn out, other carbon nanotube segments are alsodrawn out end to end due to van der Waals force between ends of adjacentsegments. This process of pulling produces a substantially continuousand uniform carbon nanotube film having a predetermined width.

After the step (b2), the drawn carbon nanotube film can be treated byapplying an organic solvent to the drawn carbon nanotube film to soakthe entire surface of the carbon nanotube film. The organic solvent isvolatile and can be ethanol, methanol, acetone, dichloromethane,chloroform, or any appropriate mixture thereof. In one embodiment, theorganic solvent is ethanol. After being soaked by the organic solvent,adjacent carbon nanotubes in the carbon nanotube films that are able to,bundle together due to the surface tension of the organic solvent as theorganic solvent volatilizes. In another aspect, due to the decrease ofthe specific surface area from the bundling, the mechanical strength andtoughness of the drawn carbon nanotube film are increased and thecoefficient of friction of the carbon nanotube films is reduced.Macroscopically, the drawn carbon nanotube film will be an approximatelyuniform film.

A width of the drawn carbon nanotube film depends on the size of thecarbon nanotube array. A length of the drawn carbon nanotube film can beset as desired. In one embodiment, when the substrate is a 4 inch typewafer, the width of the carbon nanotube film can be in a range fromabout 1 centimeter to about 10 centimeters, and the length of the carbonnanotube film can reach to about 120 meters. The thickness of the drawncarbon nanotube film can be in a range from about 0.5 nanometers toabout 100 micrometers. Multiple films can be adhered together to obtaina film of any desired size.

If the carbon nanotube structure includes a number of stacked drawncarbon nanotube films, and the stacked drawn carbon nanotube films canbe fabricated by:

(1) providing a number of drawn carbon nanotube films, adhering onedrawn carbon nanotube film to a frame;

(2) depositing other drawn carbon nanotube films on the preceding drawncarbon nanotube film successively, thereby achieving at least atwo-layer drawn carbon nanotube film; and

(3) peeling the stacked drawn carbon nanotube films off the frame toachieve the stacked drawn carbon nanotube films.

The carbon nanotubes in the pressed carbon nanotube film are arrangedalong a same direction or along different directions. The carbonnanotubes in the pressed carbon nanotube film can rest upon each other.A method of making the pressed carbon nanotube film includes:

(b1′) providing a carbon nanotube array and a pressing device; and

(b2′) pressing the carbon nanotube array to obtain a pressed carbonnanotube film.

In the step (b1′), the carbon nanotube array can be made by the samemethod as the step (b1).

In the step (b2′), a certain pressure can be applied to the carbonnanotube array by the pressing device. In the process of pressing, thecarbon nanotubes of the carbon nanotube array separate from thesubstrate and obtain the carbon nanotube film under pressure. The carbonnanotubes are substantially parallel to a surface of the carbon nanotubefilm.

In one embodiment, the pressing device can be a pressure head. Thepressure head has a smooth surface. The shape of the pressure head andthe pressing direction can determine the direction of the carbonnanotubes arranged therein. When a pressure head (e.g. a roller) is usedto travel across and press the array of carbon nanotubes along apredetermined single direction, a carbon nanotube film having a numberof carbon nanotubes substantially aligned along a same direction isobtained. It can be understood that there may be some variation in thefilm. Different alignments can be achieved by applying the roller indifferent directions over an array. Variations on the film can alsooccur when the pressure head is used to travel across and press thearray of carbon nanotubes several times, as variations will occur in theorientation of the nanotubes. Variations in pressure can also achievedifferent angles between the carbon nanotubes and the surface of thesubstrate on the same film. If a planar pressure head is used to pressthe array of carbon nanotubes along the direction perpendicular to thesubstrate, a carbon nanotube film having a number of carbon nanotubesisotropically arranged can be obtained. If a roller-shaped pressure headis used to press the array of carbon nanotubes along a certaindirection, a carbon nanotube film having a number of carbon nanotubesaligned along the certain direction is obtained. If a roller-shapedpressure head is used to press the array of carbon nanotubes alongdifferent directions, a carbon nanotube film having a number of sectionshaving carbon nanotubes aligned along different directions is obtained.

The flocculated carbon nanotube film can include a number of long,curved, disordered carbon nanotubes entangled with each other.Furthermore, the flocculated carbon nanotube film can be isotropic. Theflocculated carbon nanotube film can be made by:

(b1″) providing a carbon nanotube array;

(b2″) separating the carbon nanotube array from the substrate to obtaina number of carbon nanotubes;

(b3″) adding the carbon nanotubes to a solvent to obtain a carbonnanotube floccule structure in the solvent; and

(b4″) separating the carbon nanotube floccule structure from thesolvent, and shaping the separated carbon nanotube floccule structureinto a carbon nanotube film to achieve a flocculated carbon nanotubefilm.

In the step (b1″), the carbon nanotube array can be fabricated by thesame method as the step (b1).

In the step (b2″), the carbon nanotube array is scraped off thesubstrate to obtain the carbon nanotubes. The length of the carbonnanotubes can be less than 10 micrometers.

In the step (b3″), the solvent can be selected from water or volatileorganic solvent. After adding the carbon nanotubes to the solvent, aprocess of flocculating the carbon nanotubes can be executed to createthe carbon nanotube floccule structure. The process of flocculating thecarbon nanotubes can be ultrasonic dispersion of the carbon nanotubes oragitating the carbon nanotubes. In one embodiment, ultrasonic dispersionis used to flocculate the solvent containing the carbon nanotubes fromabout 10 minutes to about 30 minutes. Due to the carbon nanotubes in thesolvent having a large specific surface area and the tangled carbonnanotubes having a large van der Waals force, the flocculated andtangled carbon nanotubes obtain a network structure (e.g., flocculestructure).

In the step (b4″), the process of separating the floccule structure fromthe solvent includes:

(b4″1) filtering out the solvent to obtain the carbon nanotube flocculestructure; and

(b4″2) drying the carbon nanotube floccule structure to obtain theseparated carbon nanotube floccule structure.

In the step (b4″1), the carbon nanotube floccule structure can bedisposed in room temperature for a period of time to dry the organicsolvent therein.

In the step (b4″2), the process of shaping includes:

(b4″21) putting the separated carbon nanotube floccule structure on asupporter, and spreading the carbon nanotube floccule structure toobtain a predetermined structure;

(b4″22) pressing the spread carbon nanotube floccule structure with adetermined pressure to yield a desirable shape; and

(b4″23) removing the residual solvent contained in the spread flocculestructure to obtain the flocculated carbon nanotube film.

Through flocculating, the carbon nanotubes are tangled together by vander Waals force to obtain a network structure/floccule structure. Thus,the flocculated carbon nanotube film has good tensile strength.

In one embodiment, the carbon nanotube structure 304 is a drawn carbonnanotube film. The carbon nanotube structure 304 is disposed on thesurface 301 of the substrate 300.

In the step (c), a power of the electromagnetic waves can be in a rangefrom about 300 watts to about 2000 watts. A melting point of thesubstrate 300 determines the power and an exposure period of theelectromagnetic waves. The higher the melting point of the substrate300, the higher the power or the longer exposure period of theelectromagnetic waves. The electromagnetic waves can be radio frequency,microwaves, near infrared, or far infrared. In one embodiment, theelectromagnetic waves are microwaves. A power of the microwaves can bein a range from about 300 watts to about 1500 watts. A frequency of themicrowaves can be in a range from about 1 gigahertz to about 5gigahertz. The carbon nanotube structure 304 and the substrate 300 arekept and are heated in the chamber filled with the microwaves from about1 second to about 300 seconds. In other embodiments, the carbon nanotubestructure 304 and the substrate 300 are kept and are heated in thechamber filled with the microwaves from about 3 seconds to about 90seconds. The time period the carbon nanotube structure 304 and thesubstrate 300 are heated in the chamber filled with the microwavesdepends on the substrate 300 and the power of the microwaves. The higherthe power of the microwaves, the shorter the time the chamber needs tobe filled with the microwaves. In one embodiment, the time is about 30seconds.

In addition, in the step (c), the carbon nanotube structure 304 isexposed to the electromagnetic waves until a portion of the substrate300 is melted and permeates into the micro gaps defined by the carbonnanotube structure 304. In one embodiment, the carbon nanotube structure304 disposed on the surface 301 of the substrate 300 can be placed intoa chamber filled with the electromagnetic waves. In one embodiment, thematerial of the substrate 300 is a polymer and barely absorbs theelectromagnetic wave energy. Thus, the substrate 300 will not be heatedby the electromagnetic waves. The carbon nanotube structure 304 disposedon the surface 301 of the substrate 300 can absorb the energy of themicrowaves and generate heat. Because the carbon nanotube structure 304has a small heat capacity per unit area, a temperature of the carbonnanotube structure 304 rises quickly. This temperature increase willheat the surface 301 of the substrate 300 until the carbon nanotubestructure 304 is able to infiltrate the substrate 300. In oneembodiment, the heat melts the surface 301 of the substrate 300, and aliquid substrate is present on the surface 301. Because the wettabilityof the melted liquid substrate and the carbon nanotube structure 304 isgood, the melted liquid substrate will infiltrate into micro gapsdefined by the carbon nanotube structure 304, as such, the carbonnanotube structure 304 will be coated by the melted liquid substrate.After the melted liquid substrate wets the whole carbon nanotubestructure 304, the material of the substrate 300 will stop moving intothe micro gaps and the micro gaps will be full of the material of thesubstrate 300.

The carbon nanotube structure 304 settles into the substrate 300 below asurface 302 of the substrate 300, as shown in FIG. 3 and FIG. 4. Thus,the carbon nanotube structure 304 is disposed in the substrate 300. Athickness of part of the substrate 300 above the carbon nanotubestructure 304 between the surface 302 of the substrate 300 and thecarbon nanotubes of the carbon nanotube structure 304 is less than 10micrometers. The heat generated by the carbon nanotube structure 304 canbe absorbed by the substrate 300, and the temperature of the carbonnanotube structure 304 can be controlled at under about 700° C., and thecarbon nanotube structure 304 will not burn.

In one embodiment, the substrate 300 is made of polyethylene, which hasa melting point of about 137° C. The carbon nanotube structure 304 andthe substrate 300 can be kept in the chamber filled with microwavesuntil the temperature of the surface 301 of the substrate 300 reaches oris a little higher than the melting point of the polyethylene. Thecarbon nanotube structure 304 and the substrate 300 can be kept in thechamber for about 10 seconds, and the carbon nanotube structure 304 willbe embedded in the substrate 300.

The step (c) can be carried out in a vacuum environment or in a specificatmosphere of protective gases including nitrogen gas and inert gases. Agas pressure of the environment is in a range from about 1*10⁻² Pascalsto about 1*10⁻⁶ Pascals. The carbon nanotube structure 304 can generatea lot of heat and reach the temperature of about 2000° C. to embed intothe substrate 300, which has high melting points when the carbonnanotube structure 304 works in the vacuum environment or in thespecific atmosphere of protective gases including nitrogen gas and inertgases.

The method for forming the carbon nanotube composite has the followingadvantages. First, only the surface of the substrate is heated to formthe carbon nanotube composite. There is no need to heat the wholesubstrate, thus the substrate will not be destroyed and energy is saved.Second, the method for forming the carbon nanotube composite canmaintain the thickness of the substrate above the carbon nanotubestructure at less than 10 micrometers. Thus, the surface of the carbonnanotube composite is conductive. Furthermore, methods described hereinfor making the carbon nanotube composite are relatively simple and easyto perform.

Referring to FIG. 3 and FIG. 4, a carbon nanotube composite 30 made bythe above method is provided. The carbon nanotube composite 30 includesa substrate 300 and a carbon nanotube structure 304. The substrate 300includes a top surface 302. The carbon nanotube structure 304 isdisposed in the substrate 300 and below the surface 302. The carbonnanotube structure 304 is near the top surface 302 of the substrate 300.A distance between the top surface 302 of the substrate 300 and thecarbon nanotube structure 304 is less than 10 micrometers. In someembodiments, the distance between the surface 302 of the substrate 300and the carbon nanotube structure 304 is in a range from about 10nanometers to about 200 nanometers.

The substrate 300 can be ceramic, glass, a polymeric material, or amacromolecular material. Examples of the polymeric material includepolyethylene, epoxy, bismaleimide resin, cyanate resin, polypropylene,polyethylene, polyvinyl alcohol, polystyrene, polycarbonate, andpolymethylmethacrylate. In one embodiment, the substrate 300 is amacromolecular material, a melting point of the substrate 300 can beless than 600° C., and a sheet resistance of the surface 302 of thesubstrate 300 is equal to or less than 8000 ohms. In another embodiment,the substrate 300 is a pure polymeric material, and the sheet resistanceof the surface 302 of the substrate 300 exceeds 8000 ohms

The carbon nanotube structure 304 includes a number of carbon nanotubescombined by van der Waals force therebetween. The carbon nanotubestructure 304 can be a substantially pure structure of the carbonnanotubes, with few impurities. A thickness of the carbon nanotubestructure 304 can be in a range from about 50 nanometers to about 10micrometers. The carbon nanotubes define a number of micro gaps havingdiameters that can be less than 10 micrometers. The micro gaps can bedefined by distances between adjacent carbon nanotubes. The carbonnanotubes of the carbon nanotube structure 304 can be orderly ordisorderly arranged.

In the carbon nanotube composite 30, the micro gaps defined of thecarbon nanotube structure 304 are filled with substrate 300. In oneembodiment, according to FIG. 5, the surface 302 of the substrate 300 isalmost a slick surface, and the carbon nanotube structure 304 is buriedbelow the surface 302. Because the substrate 300 is made of atransparent material, the carbon nanotube structure 304 can be seen fromthe surface 302. Referring to FIG. 6 and FIG. 7, in the SEM image, thecarbon nanotube structure 304 can be clearly seen. Some carbon nanotubesof the carbon nanotube structure 304 protrude from the carbon nanotubestructure 304. The carbon nanotubes protruding from the carbon nanotubestructure 304 are also coated by the material of the substrate 300.During the process, because wettability of the melted liquid substrateand the carbon nanotube structure 304 is good, the melted liquidsubstrate will infiltrate into micro gaps of the carbon nanotubestructure 304, and the carbon nanotube structure 304 will be coated bythe melted liquid substrate. A thickness of the substrate 300 coated oneach of the protruding carbon nanotubes is less than 100 nanometers. Insome embodiments, the thickness is in a range from about 20 nanometersto about 30 nanometers. In FIG. 7, the protruding carbon nanotubes ofthe carbon nanotube structure 304 are coated by the material of thesubstrate 300, and the diameters of the protruding carbon nanotubes arein a range from about 70 nanometers to about 90 nanometers. Thediameters of the carbon nanotubes without being coated by the materialof the substrate 300 are in a range from about 10 nanometers to about 30nanometers. As such, the thickness of the substrate 300 coated onsurfaces of the protruding carbon nanotubes is about 30 nanometers.

Referring to FIG. 8, image A, a water drop is applied on a surface ofthe carbon nanotube structure 304, including a drawn carbon nanotubefilm disposed on the surface of the substrate 300. The water drop willspread on the carbon nanotube structure 304 along a direction of thecarbon nanotubes to form an elliptical structure having an area of about5.69 mm² because the carbon nanotubes in the drawn carbon nanotube filmare oriented in a same direction. Referring to FIG. 8, image B, afterthe carbon nanotube structure 304 and the substrate 300 are heated bythe microwaves, the carbon nanotube structure 304 is buried under thesurface 302. After the water drop has dropped on the surface 302, thewater drop will spread to form a round structure having an area of about5.14 mm².

In one embodiment, because the substrate 300 is the macromolecularmaterial and the thickness of the substrate 300 above the carbonnanotube structure 304 is less than 10 micrometers, the surface 302 ofthe carbon nanotube composite 30 is conductive. A sheet resistance ofthe surface 302 of the substrate 300 is equal to or less than 8000 ohms.The sheet resistance of the surface 302 of the substrate 300 is about5000 ohms. In another embodiment, because the substrate 300 is a purepolymeric material, the sheet resistance of the surface 302 of thesubstrate 300 exceeds 8000 ohms. Furthermore, referring to FIG. 9, thesheet resistance of the surface 302 of the substrate 300 can be about400 ohms by adjusting layers of the carbon nanotube structure 304.

An experiment proved that the conductivity of the surface 302 is notaffected by friction from the outside. The experiment is performed onone embodiment of the carbon nanotube composite 30, according to thefollowing steps:

providing the carbon nanotube composite 30, wherein the carbon nanotubecomposite 30 is a cuboid, and an area of the surface 302 is about 64mm²;

applying two electrodes on the opposite sides of the surface 302 tomeasure the sheet resistance; and

scraping the surface 302 with a tip of a needle with a pressure force ofabout 0.7 Newton between the two electrodes, wherein the needle has atip covered by cotton.

During the scraping step, the two electrodes are used to measure thesheet resistance, and the sheet resistance changes less than 10% afterscraping the surface 302 about 50 times. On the contrary, if the carbonnanotube structure 304 is disposed on the surface 302 of the substrate300 without exposure to the microwaves, the needle would easily destroythe carbon nanotube structure 304. Thus, the sheet resistance wouldrapidly change.

Referring to FIG. 10, a method for forming an electrode board includes:

(a) providing a carbon nanotube composite; and

(b) disposing two electrodes between opposite sides of the carbonnanotube composite.

In the step (a), the carbon nanotube composite is the carbon nanotubecomposite 30 as shown in FIG. 3 and FIG. 4. A material of the electrodescan be metal, carbon nanotube films, silver paste, or any conductivematerial. In one embodiment, silver paste is applied on the oppositesides of the carbon nanotube composite and then dried at a temperaturein a range from about 100° C. to about 120° C. for about 10 minutes toabout 60 minutes. Thus, the electrodes are formed.

In the step (b), the electrodes are electrically connected to the carbonnanotube composite 30 to form the electrode board. A method ofelectrically connecting the electrodes to the carbon nanotube composite30 includes the steps of:

(b1) removing a part of the surface of the substrate to expose a part ofthe carbon nanotube structure; and

(b2) disposing the electrodes on the exposed carbon nanotube structure.

Referring to FIG. 11, a method for forming an electrode board includes:

(a) providing a substrate having a surface;

(b) disposing a carbon nanotube structure on the surface of thesubstrate;

(c) disposing two electrodes between opposite sides of the carbonnanotube structure; and

(d) disposing the substrate, the carbon nanotube structure, and theelectrodes in an environment filled with electromagnetic waves.

In the step (b), the carbon nanotube structure includes a number ofcarbon nanotubes combined by van der Waals force therebetween. Thecarbon nanotubes define a number of micro gaps. In addition, the step(d) of the method for forming an electrode board is the same as the step(c) of the method for forming a carbon nanotube composite.

Referring to FIG. 12, an electrode board 20 made by the above methods isalso provided. The electrode board 20 includes a substrate 300, a carbonnanotube structure 304, and two electrodes 202. The substrate 300 andthe carbon nanotube structure 304 form the carbon nanotube composite 30.The substrate 300 includes a top surface 302, the carbon nanotubestructure 304 is disposed in the substrate 300 and below the surface302. The carbon nanotube structure 304 is near the top surface 302 ofthe substrate 300. The electrodes 202 are disposed between oppositesides of the carbon nanotube composite 30 and are electrically connectedto the carbon nanotube composite 30.

Referring to FIG. 13, a method for forming a touch panel includes:

(a) preparing a first electrode board;

(b) preparing a second electrode board; and

(c) packaging the first electrode board and the second electrode boardto form a touch panel.

In the step (a), the first electrode board includes a first substrate, afirst carbon nanotube structure, and two first electrodes. In the step(b), the second electrode board includes a second substrate, a secondcarbon nanotube structure, and two second electrodes.

In the step (c), a method of packaging the first electrode board and thesecond electrode board includes the steps of:

(c1) applying an insulating layer around sides of a surface of thesecond substrate of the second electrode board;

(c2) covering the first electrode board on the insulating layer suchthat the first carbon nanotube structure of the first electrode boardand the second carbon nanotube structure of the second electrode boardare disposed face to face; and

(c3) sealing the first electrode board, the second electrode board, andthe insulating layer with sealant to form the touch panel.

The first carbon nanotube structure includes at least one carbonnanotube film. Similarly, the second carbon nanotube structure includesat least one carbon nanotube film. The carbon nanotube film can be adrawn carbon nanotube film, a pressed carbon nanotube film, or aflocculated carbon nanotube film.

Referring to FIG. 14, a touch panel 10 can be made by the above method.The touch panel 10 includes a first electrode board 12, a secondelectrode board 14, a number of transparent spaces 16, and an insulatinglayer 18. The transparent spaces 16 are disposed between the firstelectrode board 12 and the second electrode board 14. The insulatinglayer 18 is disposed around sides of a surface of the second electrodeboard 14 near the first electrode board 12.

Furthermore, referring to FIG. 15, the first electrode board 12 includesa first substrate 120, a first carbon nanotube structure 122, and twofirst electrodes 124. The first substrate 120 is planner. The firstcarbon nanotube structure 122 and the first electrodes 124 are disposedon a bottom surface of the first substrate 120. The first electrodes 124are respectively disposed on two sides of the first electrode board 12along a first direction, and are electrically connected to the firstelectrode board 12. The second electrode board 14 includes a secondsubstrate 140, a second carbon nanotube structure 142, and two secondelectrodes 144. The second substrate 140 is planner. The second carbonnanotube structure 142 and the second electrodes 144 are disposed on atop surface of the second substrate 140. The second electrodes 144 arerespectively disposed on two sides of the second electrode board 14along a second direction, and are electrically connected to the secondelectrode board 14. The first direction is substantially perpendicularto the second direction.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the present disclosure.Variations may be made to the embodiments without departing from thespirit of the disclosure as claimed. Elements associated with any of theabove embodiments are envisioned to be associated with any otherembodiments. The above-described embodiments illustrate the scope of thedisclosure but do not restrict the scope of the disclosure.

It is also to be understood that above description and the claims drawnto a method may include some indication in reference to certain steps.However, the indication used is only to be viewed for identificationpurposes and not as a suggestion as to an order for the steps.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

1. A method for forming a carbon nanotube composite, comprising:providing a substrate having a surface; disposing a carbon nanotubestructure on the surface of the substrate, wherein the carbon nanotubestructure comprises a plurality of carbon nanotubes defining a pluralityof micro gaps; and disposing the substrate and the carbon nanotubestructure in an environment filled with electromagnetic waves to meltthe surface of the substrate such that the melted surface of thesubstrate is permeated into the plurality of micro gaps.
 2. The methodas claimed in claim 1, wherein the surface of the substrate is planar ora curved surface.
 3. The method as claimed in claim 1, wherein a meltingpoint of the substrate is less than 600° C.
 4. The method as claimed inclaim 1, wherein a power of the electromagnetic waves is in a range fromabout 300 watts to about 2000 watts.
 5. The method as claimed in claim1, wherein the electromagnetic waves are microwaves, a power of themicrowaves is in a range from about 300 watts to about 1500 watts, and afrequency of the microwaves is in a range from about 1 gigahertz toabout 5 gigahertz.
 6. The method as claimed in claim 5, wherein thesubstrate and the carbon nanotube structure are disposed in theenvironment for about 1 second to about 300 seconds.
 7. The method asclaimed in claim 1, wherein the step of disposing the carbon nanotubestructure on the surface of the substrate further comprises: preparing afree-standing carbon nanotube structure; and laying the free-standingcarbon nanotube structure on the surface of the substrate.
 8. The methodas claimed in claim 7, wherein the step of disposing the carbon nanotubestructure on the surface of the substrate further comprises: soaking thefree-standing carbon nanotube structure with organic solvent; and dryingthe free-standing carbon nanotube structure after being soaked with theorganic solvent.
 9. The method as claimed in claim 1, wherein a gaspressure of the environment is in a range from about 1*10⁻² Pascals toabout 1*10⁻⁶ Pascals.
 10. The method as claimed in claim 1, wherein anaperture of each of the plurality of micro gaps is equal to or less than10 micrometers, and the carbon nanotube structure heats the surface ofthe substrate to melt the surface of the substrate such that the meltedsurface of the substrate permeates into the plurality of micro gaps. 11.The method as claimed in claim 10, wherein a material of the substratecoats on each of the plurality of carbon nanotubes of the carbonnanotube structure after being melted.
 12. A carbon nanotube composite,comprising: a substrate having a surface; and a carbon nanotubestructure disposed in the substrate, wherein a distance between thesurface of the substrate and the carbon nanotube structure is equal toor less than 10 micrometers.
 13. The carbon nanotube composite asclaimed in claim 12, wherein a material of the substrate is selectedfrom the group consisting of epoxy, bismaleimide resin, cyanate resin,polyethylene, polypropylene, polystyrene, polyvinyl alcohol,polycarbonate, and polymethylmethacrylate.
 14. The carbon nanotubecomposite as claimed in claim 12, wherein a melting point of thesubstrate is less than 600° C.
 15. The carbon nanotube composite asclaimed in claim 12, wherein the carbon nanotube structure comprises aplurality of carbon nanotubes defining a plurality of micro gaps. 16.The carbon nanotube composite as claimed in claim 15, wherein theplurality of micro gaps are filled with the substrate.
 17. The carbonnanotube composite as claimed in claim 15, wherein the plurality ofcarbon nanotubes are entangled with each other.
 18. The carbon nanotubecomposite as claimed in claim 15, wherein the plurality of carbonnanotubes are arranged approximately along a same direction.
 19. Acarbon nanotube composite, comprising: a substrate having a surface; anda carbon nanotube structure disposed in the substrate, wherein amaterial of the substrate is a macromolecular material, and a sheetresistance of the surface of the substrate is equal to or less than 8000ohms.
 20. The carbon nanotube composite as claimed in claim 19, whereina distance between the surface of the substrate and the carbon nanotubestructure is equal to or less than 10 micrometers.